Effects Of Sulfur Application On Accumulation Of Cadmium In Rice(Oryza Sativa L.)Under Different Soil Moisture Conditions

Cadmium?Cd?contamination in paddy soils and the related pollution risk of rice grain have received increasing attention.Adopt field water management and sulfur application cadmium accumulation had to conduct more extensive studies.However,the study on cadmium uptake in rice to be strengthened with the coupling regulation of application the sulfur and water management.Therefore,taking cadmium-contaminated rice soil as an object,through pot experiment and root bag cultivation measures,research continuous flooding?F?,flooding-moist alternation?FM?and moist irrigation?M?water management mode,the three kinds of elemental sulfur?S⁰?and sulfate(S^?)the regulation effect of cadmium uptake of rice accumulated,and combined with the change of soil physical and chemical properties,formation of iron plaque of rice root surface and fixation of cadmium,and the mechanism of action was discussed.The main research results are as follows:?1?There was no significant difference in the effect of different water management on the biomass of rice.However,the cadmium content in each organ of rice decreased with the increase of water,showing a trend of F<FM<M.Under the water management F,S^?treatment had the lowest Cd content in rice,with a decrease of 15.7%?41.6%.The decrease of S^?treatment was the largest in water managemen M,with a range of35.5%?56.3%,the water managemen FM in between.The effect of S⁰was relatively small on Cd content of mature rice,only when S⁰treatment dosage reached 30 and 40mg/kg,Cd content of rice decreased significantly,by 17.7%and 25.2%.?2?In different growth periods,the application of two exogenous sulfurs significantly affected the absorption of Cd in rice.Application of S^?at the tillering stage had little effect on the roots of rice,but reduced the TF_{aboveground/root}transport by14.2%?58.0%.Nevertheless,the application of S⁰significantly increased the content of root cadmium by 54.0?84.8%,while the transport of TF_{aboveground/root}decreased by0.8%-55.4%.During the ripening period,the cadmium content in rice roots increased by10.4%-17.0%when S^?was applied,and the transport of TF_straw/rootand TF_grain/rootdecreased by 12.9%-52.8%and 7.1%-54.7%respectively.However,the cadmium content of roots increased significantly 23.6%?71.9%with the application of S⁰,while the transport of TF_straw/rootand TF_grain/rootdecreased by 0.6%?54.6%and 6.0%?41.3%.?3?During the whole growth period of rice,soil p H showed the law of F>FM>M under different water management,and the soil p H of non-rhizosphere was higher than that of rhizosphere.At tillering stage,grain filling stage and maturation stage,the application of S^?will increase the p H of rhizosphere soil,with a maximum increase of0.97-2.31 units,and a maximum decrease of 0.54-1.06 units in non-rhizosphere p H.Application of S^?reduced the content of effective state Cd in rhizosphere by up to45.3%-57.5%.There was no consistent law of soil p H and available Cd in three periods.Application of S^?treatment can increase the biomass of rice to a certain extent.The content of DCB-Fe and DCB-Mn the highest increased by 72.9%and 49.4%of iron plaque of rice root surface.The increase of Fe and Mn contents in the iron plaque of rice root surface also promoted the absorption of Cd by the rice root,which make the most of the Cd accumulation in rice root surface and within the root,reduced the transfer of Cd from root to rice,and thus reduced the accumulation of Cd in rice.In conclusion,water management combined with S^?can effectively reduce the available Cd in rhizosphere soil.It promotes the formation of iron plaque of rice root surface and the fixation of Cd,prevents the transfer of Cd from rice to overground,and reduces the accumulation of Cd in rice.